1. Field of the Invention
The present invention relates to a tone signal generator which can generate tone signals to which various specialized sound effects such as modulation and pitch change are provided, along with musical tones and normal sound effects.
2. Description of the Prior Art
TV game instruments for entertainment in practical use have a tone signal generator. In this instrument, data of tone signals stored in a game cartridge provided by a ROM or a CD-ROM is supplied into an internal RAM of the game instrument, and the data is read according to progress of a game program carried out for generating musical tones with the normal sound effects and the musical tones as back ground music.
The above musical tones for the TV game instruments or the like involve various specialized sound effects, such as modulation, for entertainment of the game. In order to obtain advantages of the sound effects, some coefficients supplied to the tone signal generator are required. The coefficients are used for deciding a level of the sound effects and drifting the level thereof.
The prior tone signal generators have been provided with LFOs (Low Frequency Oscillators) and modulation signal generation circuits used for only generating the coefficients.
Generally, a DSP (digital Signal Processor) chip is used to generate the sound effects. In the DSP, it is necessary to prepare signal data to be parameters for filtering and modulating. For example, in case of modulating, the signal data for the modulating is required. Therefore, the prior tone signal generators have been provided with a circuit which has many functions to generate various kinds of the signal data.
Furthermore, it is possible to prepare a plurality of groups of coefficients in advance for filtering, and to change the present group dynamically to allow the tone signal generator to generate various sound effects. Therefore, the prior tone signal generators are provided with a filter device using a DSP chip schematically shown in FIG. 18.
In FIG. 18, a plurality of filter coefficients (a to d) are supplied from a filter coefficient register R to a DSP 71, and the DSP 71 uses a set of the coefficients for filtering to a filter input signal Si in one sample process time. In dynamically changing the filter coefficients, a CPU 70 changes the coefficients stored in the coefficient register R with time. In this case, writing the coefficients from the CPU 70 to the coefficient register R is performed successively in time series according to a process clock of the CPU 70. Therefore, a certain extent of time is required to replace the present set of the coefficients in the coefficients register R with a new set of the coefficients.
The prior tone signal generators, however, have disadvantages in that they need discrete hard circuits, such as the LFO and the modulation signal generation circuit, resulting in complex constitution of a whole circuit, large-sized LSI, and cost-up. Still more, it is difficult to obtain complex sound effects. Therefore, there is a limitation of the sound effects in each game program.
Furthermore, the prior tone signal generators having a circuit for the functions of generating various kinds of the signal data have another disadvantage in that the whole circuit becomes more complex, larger and more expensive.
Still more, in the filter configuration of the prior tone signal generator, re-writing of the coefficients causes conflicts of the filtering process. For instance, if the group of coefficients a-d is changed to the group of coefficients e-h in the coefficient register R, the coefficients of the two groups are mixed till the whole coefficients changing is finished. This mixed state makes the DSP wrong filtering process, therefore causing noises into a filter output signal So and oscillations of the DSP.